While fixing my girlfriend's daughter's computer I found gay a?

She is 15 years old and her PC laptop received a bad trojan from using Limewire. It affected the bulk of her files and looking at which ones were corrupted I found she had a rather large folder of gay a files, you know like literary ? Not or anything, these were stories of men having (and I'll admit, I read a bit of one, curiousity got the better of me, and in the one they were teenage boys. Juniors in high school, 17. Is that even legal?) Should I tell my girlfriend? She's way too young to know about this kind of stuff and if it were one of my daughters I'd want to know. Or Should I just forget about it? She's a very well rounded, intelligent, sociable girl, not a problem child or misfit/deliquent at all, so maybe it's just a harmless interest of hers? I don't know what to do.